Process and system for dehydrating a product stream in ethanol production

ABSTRACT

The present disclosure provides processes and systems for dehydrating a byproduct stream in ethanol production. In one embodiment, a feed mixture is distilled with one or more distillation units to remove at least a portion of the water, and form a first byproduct stream. The first byproduct stream is contacted with a molecular sieve unit, thereby forming a product stream. The molecular sieve unit is cyclically contacted with at least a portion of the product stream to regenerate the molecular sieve unit and form one or more regenerate streams. A second byproduct stream including at least one of (1) the regenerate streams and (2) at least a portion of the fusel oil stream is contacted with a separation system, thereby forming a permeate and a retentate. At least a portion of the retentate is forwarded into the product stream.

REFERENCE TO PENDING PRIOR PATENT APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 15/400,546 filed on Jan. 6, 2017 which claims the benefit ofU.S. Provisional Patent Application No. 62/432,008, filed on Dec. 9,2016, and U.S. Provisional Patent Application No. 62/276,318, filed onJan. 8, 2016, the entire contents of each of which are herebyincorporated herein by reference.

BACKGROUND

Various processes and systems have been used for producing ethanol fromfeedstock. For example, in some prior systems, ethanol is produced byfermentation, yielding a stillage (beer) with an ethanol concentrationof up to 18%, which is subsequently concentrated in three steps: (1)distillation in a beer column, increasing the ethanol concentration upto 65%, followed by (2) processing in a stripper/rectifier columnfurther increasing the ethanol concentration to around 90 vol %, and (3)a molecular-sieve-based dehydration (also referred to as pressure swingadsorption) to a target ethanol concentration of 99.0 to 99.95 vol %. Inthe stripper/rectifier column, a mixture of high boiling componentsincluding propanol, butanol, and isomeric pentanols (also referred to asfusel oil) needs to be removed in a side draw to avoid accumulationtherein.

SUMMARY

According to one non-limiting aspect of the present disclosure, anexample embodiment of a method of dehydrating a byproduct stream inethanol production is described. The example method includes distillinga feed mixture including ethanol and water with one or more distillationunits to remove at least a portion of the water, and form a distillationunit bottom stream, a vaporous overhead stream, and a fusel oil stream.A molecular sieve unit is contacted with a first byproduct streamincluding at least one selected from a portion of the vaporous overheadstream and a portion of the fusel oil stream, thereby forming a productstream. The molecular sieve unit is cyclically contacted with at least aportion of the product stream to regenerate the molecular sieve unit andform one or more regenerate streams. A second byproduct stream includingat least one of (1) the regenerate stream and (2) at least a portion ofthe fusel oil stream is contacted with a separation system, therebyforming a permeate and a retentate. At least a portion of the permeateis forwarded into the second byproduct stream. Heat is exchanged betweenat least a portion of the retentate and at least one selected from thefeed mixture, the distillation unit bottom stream, the first byproductstream, and a portion of the regenerate streams.

In certain non-limiting embodiments of the method, a scrubbing system isused to remove ethanol from vent gases (e.g., CO₂, with traces ofethanol) from the fermentation stream separating the ethanol from CO₂before venting to the atmosphere. Scrubber water is added in thescrubbing system generating a water stream containing small amounts ofethanol which is directed to the beer well prior to being fed to thebeer column. At least a portion of the product stream is forwarded to aflash vessel, thereby forming a vent stream. A second byproduct streamincluding at least one of (1) a portion of the regenerate streams, (2) aportion of the first byproduct stream, (3) a portion of the fusel oilstream, (4) a portion of the vent stream and (5) a portion of thescrubber water stream is contacted with a separation system, therebyforming a permeate, a retentate, and a stripper unit bottom stream. Incertain non-limiting embodiments of the method, at least a portion ofthe permeate is forwarded into the second byproduct stream. Heat isexchanged between at least a portion of the retentate and at least oneselected from the feed mixture, the distillation unit bottom streams,the first byproduct stream, evaporators and a portion of the regeneratestreams.

In certain non-limiting embodiments of the method, heat is exchangedbetween at least a portion of the stripper unit bottom stream and atleast one selected from the group consisting of the feed mixture, thedistillation unit bottom streams, the first byproduct stream, and aportion of the regenerate streams. According to another non-limitingaspect of the present disclosure, heat is exchanged between at least aportion of at least one of the regenerate streams and at least oneselected from the feed mixture, the distillation unit bottom streams,and the first byproduct stream.

According to another non-limiting aspect of the present disclosure,steam generated in at least one of (1) evaporators, (2) a hydroheater,and (3) a boiler is injected to the distillation units as energy sourcefor their operation. The steam injected in the distillation unitsincreases the water content and dilutes the solids contained in thedistillation unit bottom streams. The solids in distillation unit bottomstreams are recovered in at least one selected from a centrifuge, adryer, and the evaporators. In certain non-limiting embodiments of themethod, at least a portion of the steam injected on the distillationunits is replaced by reboiling at least one selected from a portion ofthe beer column stillage stream and the stripper-rectifier bottomstream. In certain non-limiting embodiments of the method, the energydisplaced in the distillation units by forwarding at least a portion ofthe regenerate streams into the second byproduct stream allows toforward (1) at least a portion of the steam from the hydroheater intothe evaporators, and (2) steam from the evaporators to the distillationunits.

According to another non-limiting aspect of the present disclosure, anexample embodiment of a system for dehydrating a byproduct stream inethanol production is described. The system includes one or moredistillation units configured to receive a feed mixture includingethanol and water, to remove at least a portion of the water, and toform a distillation unit bottom streams, a vaporous overhead stream, anda fusel oil stream. A molecular sieve unit is configured to contact afirst byproduct stream including at least one selected from a portion ofthe vaporous overhead stream and a portion of the fusel oil stream. Themolecular sieve unit is configured to form a product stream. Themolecular sieve unit is configured to be cyclically contacted with atleast a portion of the product stream to regenerate the molecular sieveunit and form one or more regenerate streams. A separation system isconfigured to contact a second byproduct stream including at least oneof (1) the regenerate streams and (2) at least a portion of the fuseloil stream, thereby forming a permeate and a retentate. A line is influid communication with the separation system to forward at least aportion of the retentate into the product stream.

In certain non-limiting embodiments of the system, the separation systemis configured to contact a second byproduct stream including at leastone of (1) a portion of the regenerate streams, (2) a portion of thefirst byproduct stream, (3) a portion of the fusel oil stream, (4) aportion of the vent stream and (5) a portion of the scrubber water,thereby forming a permeate and a retentate. A line is in fluidcommunication with the separation system to forward at least a portionof the retentate into one of the product stream and the first byproductstream.

According to another non-limiting aspect of the present disclosure, amembrane unit is configured to contact a stream including at least oneof a vaporized first byproduct steam and a portion of the vaporousoverhead stream.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the processes and systems described hereinmay be better understood by reference to the accompanying drawings inwhich:

FIG. 1 is a schematic illustration of a non-limiting example embodimentof a system for dehydrating a byproduct stream in ethanol productionaccording to the present disclosure.

FIG. 2 is a schematic illustration of another non-limiting exampleembodiment of a system for dehydrating a byproduct stream in ethanolproduction according to the present disclosure.

FIG. 3 is a schematic illustration of yet another non-limiting exampleembodiment of a system for dehydrating a byproduct stream in ethanolproduction according to the present disclosure.

FIG. 4 is a schematic illustration of yet another non-limiting exampleembodiment of a system for dehydrating a byproduct stream in ethanolproduction according to the present disclosure.

FIG. 5 is a schematic illustration of yet another non-limiting exampleembodiment of a system for dehydrating a byproduct stream in ethanolproduction according to the present disclosure.

FIG. 6 is a schematic illustration of yet another non-limiting exampleembodiment of a system for dehydrating a byproduct stream in ethanolproduction according to the present disclosure.

FIG. 7 is a schematic illustration of yet another non-limiting exampleembodiment of a system for dehydrating a byproduct stream in ethanolproduction according to the present disclosure.

The reader will appreciate the foregoing details, as well as others,upon considering the following detailed description of certainnon-limiting embodiments of processes and systems according to thepresent disclosure. The reader may also comprehend certain of suchadditional details upon using the processes and systems describedherein.

DETAILED DESCRIPTION

Prior systems for producing ethanol from feedstock typically requiremolecular sieve units (MSUs) for dehydrating the feed vapor coming fromthe stripper/rectifier column or a dedicated vaporizer. The MSUs includetwo or three beds filled with zeolite pellets, which adsorb water toproduce anhydrous vapor until they are saturated with water. While thefirst bed undergoes a regeneration cycle, the feed vapor coming from thestripper/rectifier column can be switched to a second bed for continueddehydration. A portion of freshly dehydrated alcohol can be redirectedinto the first bed to remove the water from the saturated zeolite beads,forming a regenerate stream (also referred to as MSU Regen). Due to thewater desorption, the regenerate stream (also referred to as MSU Regen)has an ethanol concentration between 50 and 80 vol %, and needs to berecycled to upstream distillation for reprocessing. This operation has anumber of disadvantages. For example, as a large portion of ethanol iscontinuously recycled, (1) capacity in the upstream distillation is usedup for dehydrating the MSU Regen, (2) capacity in the MSU itself is usedup to essentially dehydrate its own regenerate stream for recycling, and(3) additional energy or steam and cooling water are required for thereprocessing of the MSU Regen. Thus, there has developed a need forprocesses and systems that overcome the limitations of the process fordehydrating a byproduct stream in ethanol production.

The present disclosure, in part, is directed to processes and systemsfor dehydrating a byproduct stream in ethanol production. A feed mixtureincluding ethanol and water is distilled with one or more distillationunits to remove at least a portion of the water, and form a distillationunit bottom stream, a vaporous overhead stream, and a fusel oil stream.At least a portion of the fusel oil stream is combined with the vaporousoverhead stream, thereby producing a first byproduct stream. The firstbyproduct stream is contacted with a molecular sieve unit, therebyforming a product stream. The molecular sieve unit is cyclicallycontacted with at least a portion of the product stream to regeneratethe molecular sieve unit and form one or more regenerate streams. Asecond byproduct stream including at least one of (1) the regeneratestreams and (2) at least a portion of the fusel oil stream is contactedwith a separation system, thereby forming a permeate and a retentate. Atleast a portion of the permeate is forwarded into the second byproductstream.

In certain non-limiting embodiments of the method, heat is exchangedbetween at least a portion of the retentate and the feed mixture. Incertain non-limiting embodiments of the method, heat is exchangedbetween the at least a portion of the retentate and the distillationunit bottom stream. In certain non-limiting embodiments of the method,heat is exchanged between at least a portion of the retentate and thefirst byproduct stream. In certain non-limiting embodiments of themethod, heat is exchanged between at least a portion of the retentateand a portion of the regenerate streams.

In certain non-limiting embodiments of the method, heat is exchangedbetween at least a portion of the stripper unit bottom stream and atleast one selected from the group consisting of the feed mixture, thedistillation unit bottom streams, the first byproduct stream, and aportion of the regenerate streams. In certain non-limiting embodimentsof the method, heat is exchanged between at least a portion of theregenerate streams and at least one selected from the feed mixture, thedistillation unit bottom streams, the first byproduct stream, a feedcondensation system, and the second byproduct stream.

Referring to FIG. 1, the illustrated embodiment of the system orproduction plant 100 for dehydrating a byproduct stream in ethanolproduction includes a plurality of distillation units 110, an MSU 120,and a separation system 130. The plurality of distillation units 110 areconfigured to receive a feed mixture 140 including ethanol and water, toremove at least a portion of the water, and form a distillation unitbottom stream 142, vaporous overhead stream 150, and a fusel oil stream160. A “fusel oil” as used herein includes definitions that aregenerally known in the chemical engineering art, and can refer to amixture of high boiling components including propanol, butanol, andisomeric pentanols.

In certain non-limiting embodiments, the distillation unit 110 includesa beer column 170 and a stripper/rectifier column 180. In the beercolumn 170, the feed mixture 140 is distilled, increasing the ethanolconcentration up to 65%. Subsequently, in the stripper/rectifier column180 the ethanol concentration is further increased to around 90 vol %.In certain non-limiting embodiments, the beer column 170 forms a beercolumn stillage stream 172, and heat is exchanged between the beercolumn stillage stream 172 and the retentate, as further explainedbelow. Although FIG. 1 illustrates the system 100 as including twodistillation units 170, 180, in other embodiments, the system 100 mayinclude a single distillation unit or may include three or moredistillations units.

In certain non-limiting embodiments, the distillation units 110 are influid communication with one or more evaporators 144, which form anevaporator stillage stream 146. For example, the system 100 can includetwo or more, three or more, four or more, five or more, six or more,seven or more, or eight or more evaporators 144. The process and systemdescribed herein are not limited in this regard. As further explainedbelow, heat can be exchanged in the evaporators 144 between the beercolumn stillage stream 172 and at least one selected from the MSUproduct steam and the retentate (which are condensed). The beer columnstillage stream 172 can have a solids content of approximately 7%. Byexchanging heat between the beer column stillage stream 172 and the MSUproduct stream and/or retentate, some of the water in the beer columnstillage stream 172 can be evaporated, which can increase the solidscontent to become a thick stillage as the stillage travels through theevaporators 144, forming the evaporator stillage stream 146 with asolids content of approximately 35%.

In certain non-limiting embodiments, at least a portion of the fusel oilstream 160 (e.g., the vaporous portion of the fusel oil stream 162) iscombined with the vaporous overhead stream 150, thereby producing afirst byproduct stream 164. In certain non-limiting embodiments, thefirst byproduct stream 164 includes only the vaporous overhead stream150 and not the fusel oil stream 160. The MSU 120 includes one ore morebeds, and is configured to contact the first byproduct stream 164 toform a product stream 200.

With continuing reference to FIG. 1, the MSU 120 is cyclically contactedwith at least a portion of the product stream 200 to regenerate itselfand form the MSU regenerate streams 210, 212. Although FIG. 1illustrates the MSU 120 as forming two MSU regenerate streams 210, 212,in other embodiments the MSU 120 can form a single stream. In someembodiments, the first MSU regenerate stream 210 is a water-rich stream(e.g., having approximately 50% water and approximately 50% ethanol),and the second MSU regenerate stream 212 is a water-lean stream (e.g.,having approximately 3% water and approximately 97% ethanol). Theregeneration of the MSU 120 is a discontinuous desorption process,gradually removing the water by passing at least a portion of theproduct stream 200 through the bed at a substantially lower pressure(i.e., a vacuum) than was used for loading the bed for the dehydrationstep. There are both high pressure and low pressure molecular sievesystems; the regeneration of each involves use of a relative vacuumalong with anhydrous ethanol in the regeneration step. Referring to FIG.1, in the illustrated embodiment at least a portion of one of the secondMSU regenerate stream 212 is forwarded into the first byproduct stream164. In another embodiment, all of the second MSU regenerate stream 212can be forwarded in a direction away from the MSU 120.

In certain non-limiting embodiments, the separation system 130 isconfigured to contact a second byproduct stream 270 including at leastone of (1) the MSU regenerate streams 210, 212, and (2) at least aportion of the fusel oil stream 160, thereby forming a permeate 220 anda retentate 230. In certain non-limiting embodiments, at least a portionof the retentate 230 is forwarded into the product stream 200 via aretentate line 300. In certain non-limiting embodiments, a first portionof the permeate 220 is forwarded into the separation system 130 via afirst permeate line 310, and a second portion of the permeate 220 isforwarded into at least one of the distillation units 170, 180 via asecond permeate line 320. In some embodiments, the first portion of thepermeate 220 is condensed before being forwarded into the separationsystem 130. In some embodiments, the first portion of the permeate 220is condensed and combined with the second byproduct stream 270 beforebeing forwarded into the separation system 130. In some embodiments, thesecond portion of the permeate 220 is condensed before being forwardedto at least one of the distillation units 110. In some embodiments, thesecond portion of the permeate 220 is forwarded into at least one of thedistillation units 110 via direct vapor injection.

In certain non-limiting embodiments, the second byproduct stream 270includes at least a portion of the fusel oil stream 160. In someembodiments, the second byproduct stream 270 is blended with at last aportion of an overhead vent stream 280 before being contacted with theseparation system 130. For example, a flash tank 290 is in fluidcommunication with the MSU 120, and forms the overhead vent stream 280.A “vent stream” as used herein includes definitions that are generallyknown in the chemical engineering art, and can refer to a flash recyclestream resulting from the condensation of an MSU product. In certainnon-limiting embodiments, at least portion of the overhead vent stream280 is forwarded into the first byproduct stream 164. In certainnon-limiting embodiments, at least portion of the overhead vent stream280 is forwarded into the separation system via tank 420 where theenergy available in vent stream 280 can be recovered.

In certain non-limiting embodiments, the separation system 130 includesa stripper/vaporizer unit 240 and a membrane 250. The stripper/vaporizerunit 240 is configured to receive at least one of the fusel oil stream160 and the MSU regenerate streams 210, 212 and form a membrane feedvapor 260, and the membrane 250 is configured to contact the membranefeed vapor 260, thereby forming the permeate 220 and the retentate 230.In certain non-limiting embodiments, the stripper/vaporizer unit 240 isa stripper unit; in other embodiments, the stripper/vaporizer unit 240is a vaporizer unit. A stripper unit forms a pure water bottom stream,whereas a vaporizer unit forms only enriched ethanol vaporssubstantially without any bottom stream. In certain non-limitingembodiments, the permeate 220 is forwarded into the stripper unit 240 ofthe separation system 130.

In certain non-limiting embodiments, the separation system 130 ispressurized (e.g., to at least 0.3 MPa), thereby heating the retentate230. The heat contained in the vaporous retentate 230 is recuperated inan upstream heat exchanger (e.g., MSU superheater) to reduce the overallenergy consumption of the entire distillation/dehydration section of theplant 100, as further explained below.

In certain non-limiting embodiments, the membrane 250 is a polymermembrane built on a hollow fiber backbone. In certain non-limitingembodiments, a selective layer is placed on either the outside (shellside) or inside (lumen side) of the hollow fibers. In other embodiments,the membrane 250 may assume any other form, for example includingzeolites as adsorbents, so long as the membrane 250 can dehydrate themembrane feed vapor 260 to certain water contents depending on the usagerequirements or preferences for the particular system 100.

In certain non-limiting embodiments, the second byproduct stream 270defines an azeotropic ethanol concentration. An “azeotropic mixture” asused herein includes definitions that are generally known in thechemical art, and can refer to a mixture of two or more liquids in sucha way that its components cannot be altered by simple distillation.

In certain non-limiting embodiments, the retentate 230 has an ethanolconcentration higher than the azeotropic ethanol concentration.

In certain non-limiting embodiments, the separation system 130 can bepre-assembled as a unit. In this way, the separation system 130 can beinstalled to new systems 100 at final assembly, or retrofitted toexisting plants that use extractive distillation with such separationsystems. In certain non-limiting embodiments, the separation system 130is integrated without additional power (e.g., electricity) requirement,and the retentate 230 is discharged by pressure without any powersupply.

The main benefits of the dedicated separation system 130 are that it (1)frees up capacity in the main distillation, (2) reduces load to the MSU,and (3) significantly reduces the overall energy consumption of thedistillation/dehydration section. Another benefit of the dedicatedseparation system 130 is that the freed-up capacity in the distillationunits 110 and the MSU 120 can be used to increase overall productioncapacity, as the amount of the ethanol that was previously recycled asMSU regenerate streams can be supplied through the beer column 170. Forexample, the capacity of the plant 100 can be increased up to 30%without size changes to the stripper/rectifier column 180 or the MSU 120and without increasing energy consumption. Depending on the usagerequirements or preferences for the particular plant 100, the separationsystem 130 can avoid the recirculation of the MSU regenerate streams210, 212 into the stripper/rectifier column 180, rendering thedistillation units 110 less prone to fluctuations and allowing a moreefficient operation.

In certain non-limiting embodiments, the energy contained in theretentate 230 can be recuperated in the plant 100. Put another way, theplant 100 can provide upstream heat integration. In certain non-limitingembodiments, heat is exchanged between at least a portion of theretentate 230 and at least one selected from the feed mixture 140, thedistillation unit bottom stream 142, the first byproduct stream 164, anda portion of the MSU regenerate streams 210, 212. In certainnon-limiting embodiments, the heat exchange can be achieved via tie-insof lines or a heat recovery unit configured to receive at least aportion of the retentate 230 and at least one selected from the feedmixture 140, the distillation unit bottom stream 142, the firstbyproduct stream 164, the beer column stillage stream 172, and a portionof the MSU regenerate streams 210, 212. The result of this heatintegration is that energy savings in the main process are larger thanthe additional energy consumption of the separation system 130 (e.g.,30% or more), thereby reducing the overall energy consumption of theplant 100 in a compact footprint.

Referring to FIGS. 2-5, in the illustrated embodiments a scrubbingsystem 105 is used to remove ethanol from vent gases (e.g., CO₂, withtraces of ethanol) from the fermentation stream removing the ethanolbefore venting CO₂ to the atmosphere. Scrubber water is added in thescrubbing system generating a water stream 107 containing small amountsof ethanol which is directed to the beer well prior to being fed to thebeer column. At least a portion of the product stream is forwarded to aflash vessel 290, thereby forming a vent stream 503. A second byproductstream 270 including at least one of (1) a portion of the regeneratestreams 210 a, 210 b, 307, (2) a portion of the first byproduct stream164 a and 164 b, (3) a portion of the fusel oil stream 160 a and 160 b,(4) a portion of the vent stream 503 and (5) a portion of the scrubberwater 107 is contacted with the separation system 240, 250, and 420,thereby forming the permeate 220, the retentate 230, and a stripper unitbottom stream 604. In certain non-limiting embodiments of the method,heat is exchanged between a portion of the retentate 605 b and the feedmixture to the beer column. In another embodiment, heat is exchangedbetween a portion of the retentate 605 c, 605 d, 605 g and thedistillation unit bottom streams. In another embodiment, heat isexchanged between a portion of the retentate 605 f and the firstbyproduct stream. In another embodiment, heat is exchanged between aportion of the retentate 605 a and evaporators 144. In anotherembodiment, heat is exchanged between a portion of the retentate 605 eand a portion of the regenerate streams.

With continuing reference to FIG. 2, in the illustrated embodiment steamgenerated in at least one of (1) evaporators 505, (2) a hydroheater 106,and (3) a boiler is injected to the distillation units as energy sourcefor their operation. The steam injected in the distillation unitsincreases the water content and dilutes the solids contained in thedistillation unit bottom streams. The solids in distillation unit bottomstreams are recovered in at least one selected from a centrifuge 400, adryer 401, and the evaporators 144. In certain non-limiting embodimentsof the method, at least a portion of the steam injected on thedistillation units is replaced by reboiling at least one selected from aportion of the beer column stillage stream 205 and thestripper-rectifier bottom stream 206. A benefit of the reboilers is thatenergy savings can be up to 30%, and the capacity of the plant 800 canbe increased up to 30% without size changes to the stripper/rectifiercolumn and without increasing energy consumption.

Referring to FIG. 3, in the illustrated embodiment the vapor permeate220 can be integrated into the second byproduct stream. In certainnon-limiting embodiments of the method, a portion of the permeate 606 ais forwarded into the second byproduct stream via the regeneratecondensation vacuum system 410. In another embodiment, a portion of thepermeate 606 b is forwarded into the second byproduct stream via thepermeate condensation vacuum system 608. The permeate condensationsystem is designed to condense the vapor permeate and to generate thevacuum required by the membrane unit 250 in the separation system. Inanother embodiment, a portion of the permeate 606 d is forwarded intothe second byproduct stream via direct contact. In another embodiment, aportion of the permeate 606 e, 606 f, 606 g, 606 h is forwarded into thesecond byproduct stream via the distillation units. In certainnon-limiting embodiments of the method, a portion of the permeate 606 cis forwarded into the second byproduct stream via the regeneratecondensation vacuum system 410 after being condensed in a separate heatexchanger.

Referring to FIG. 4, in the illustrated embodiment the plant 820 canprovide heat integration from the stripper unit bottom stream. Incertain non-limiting embodiments of the method, heat is exchangedbetween a portion of the stripper unit bottom stream 604 a and the feedmixture. In another embodiment, heat is exchanged between a portion ofthe stripper unit bottom stream 604 b, 604 c, and 604 f and thedistillation unit bottom streams. In another embodiment, heat isexchanged between a portion of the stripper unit bottom stream 604 e andthe first byproduct stream. In another embodiment, heat is exchangedbetween a portion of the stripper unit bottom stream 604 d and a portionof the regenerate streams.

Referring to FIG. 5, in the illustrated embodiment the plant 830 canprovide heat integration from at least one of the regenerate streams(also referred to as Depressure stream). In certain non-limitingembodiments of the method, heat is exchanged between a portion of theDepressure stream 307 a and the feed mixture. In another embodiment,heat is exchanged between a portion of the Depressure stream 307 b, 307c, and 307 f and the distillation unit bottom streams. In anotherembodiment, heat is exchanged between a portion of the Depressure stream307 e and the first byproduct stream. In another embodiment, heat isexchanged between a portion of the Depressure stream 307 g and a feedcondensation system 420 which is designed to recover the energyavailable in vaporous streams including the Depressure stream. Inanother embodiment, heat is exchanged between a portion of theDepressure stream and the second byproduct stream 270 via heatexchangers 307 d.

Referring to FIG. 6, in the illustrated embodiment the energy displacedin the distillation units by forwarding at least a portion of theregenerate streams into the second byproduct stream allows to forward(1) at least a portion of the steam 505 a from the hydroheater into theevaporators, and (2) steam 506 a from the evaporators to thedistillation unit. A benefit of this energy re-balancing of the plant100 is that energy savings may be 30% or higher, and the capacity of theplant 100 may be increased 30% or higher without size changes to thestripper/rectifier column and without increasing energy consumption.

Referring to FIG. 7, in the illustrated embodiment the rectifier column202 operates as a stripper column, thereby eliminating the need of a190-proof ethanol vapor condenser and reducing the cooling waterconsumption. The beer column reboiler is operated with the overheadstream 701 from the rectifier column 202. The condensed overhead streamis processed in the separation system 240, 250. The energy in theretentate 230 is used to operate the side stripper reboiler. Theevaporators are operated at least in part with the steam 702 from thehydroheater, as the side stripper no longer needs the steam 702 from thehydroheater.

Although the foregoing description has necessarily presented only alimited number of embodiments, those of ordinary skill in the relevantart will appreciate that various changes in the processes and systemsother details of the examples that have been described and illustratedherein may be made by those skilled in the art, and all suchmodifications will remain within the principle and scope of the presentdisclosure as expressed herein and in the appended claims. For example,although the present disclosure has presented only a limited number ofembodiments of heat integration, it will be understood that the presentdisclosure and associated claims are not so limited. Those havingordinary skill will readily identify additional heat integration schemesalong the lines and within the spirit of the necessarily limited numberof embodiments discussed herein. It is understood, therefore, that thepresent inventions are not limited to the particular embodimentsdisclosed herein, but is intended to cover modifications that are withinthe principle and scope of the inventions, as defined by the claims. Itwill also be appreciated by those skilled in the art that changes couldbe made to the embodiments above without departing from the broadinventive concept thereof.

In the present description of non-limiting embodiments and in theclaims, other than in in the operating examples or where otherwiseindicated, all numbers expressing quantities or characteristics ofingredients and products, processing conditions, and the like are to beunderstood as being modified in all instances by the term “about.”Accordingly, unless indicated to the contrary, any numerical parametersset forth in the following description and the attached claims areapproximations that may vary depending upon the desired properties oneseeks to obtain in the processes and systems according to the presentdisclosure. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

We claim:
 1. A method of dehydrating a byproduct stream in ethanolproduction, the method comprising: distilling a feed mixture includingethanol and water with a distillation unit to remove at least a portionof the water, and form a distillation unit bottom stream, a vaporousoverhead stream, and a fusel oil stream; contacting a molecular sieveunit with a first byproduct stream comprising at least one selected fromthe group consisting of a portion of the vaporous overhead stream and aportion of the fusel oil stream, thereby forming a product stream;cyclically contacting the molecular sieve unit with at least a portionof the product stream to regenerate the molecular sieve unit, and form aregenerate stream; contacting a second byproduct stream comprising atleast one of (1) the regenerate stream and (2) at least a portion of thefusel oil stream with a separation system, thereby forming a permeateand a retentate; forwarding at least a portion of the retentate into theproduct stream; and exchanging heat between at least a portion of theregenerate stream and at least one selected from the feed mixture, thedistillation unit bottom streams, the first byproduct stream, thecontents of a tank, and the second byproduct stream.
 2. The method ofclaim 1, wherein the distillation unit comprises a beer column and astripper-rectifier column in fluid communication with the beer column,wherein the beer column forms a beer column stillage stream, and whereinheat is exchanged between the at least a portion of the retentate andthe beer column stillage stream.
 3. The method of claim 2, wherein thedistillation unit is in fluid communication with an evaporator, whereinthe evaporator forms an evaporator stillage stream, and wherein a secondportion of the retentate is forwarded into the evaporator.
 4. The methodof claim 1, wherein the molecular sieve unit forms only a singleregenerate stream.
 5. The method of claim 1, wherein the regeneratestream further comprises a water-rich first stream and a water-leansecond stream.
 6. The method of claim 1, wherein at least a portion ofthe regenerate stream is forwarded into the first byproduct stream. 7.The method of claim 1, wherein a first portion of the permeate isreturned to the separation system, or a second portion of the permeateis returned to the distillation unit.
 8. The method of claim 7, whereinthe first portion of the permeate is returned to the separation systemand is condensed before being returned to the separation system.
 9. Themethod of claim 7, wherein the first portion of the permeate is returnedto the separation system and is condensed and combined with the secondbyproduct stream before being returned to the separation system.
 10. Themethod of claim 7, wherein the second portion of the permeate isreturned to the distillation unit and is condensed before being returnedto the distillation unit.
 11. The method of claim 7, wherein the secondportion of the permeate is returned into the distillation unit viadirect vapor injection.
 12. The method of claim 1, wherein the secondbyproduct stream comprises at least a portion of the fusel oil stream.13. The method of claim 1, wherein a flash tank is in fluidcommunication with the molecular sieve unit, wherein the flash tankforms an overhead vent stream, and wherein the second byproduct streamis blended with at least a portion of the overhead vent stream beforebeing contacted with the separation system.
 14. The method of claim 13,wherein at least a portion of the overhead vent stream is forwarded intothe first byproduct stream.
 15. The method of claim 13, wherein theseparation system comprises a stripper unit and a membrane, the stripperunit receiving at least one of the fusel oil stream, the regeneratestream and the overhead vent stream, and forming a membrane feed vapor,and the membrane contacting the membrane feed vapor, thereby forming thepermeate and the retentate.
 16. The method of claim 15, wherein thepermeate is forwarded into the stripper unit of the separation system.17. The method of claim 13, wherein the separation system comprises avaporizer and a membrane, the vaporizer receiving at least one of thefusel oil stream, the regenerate stream and the overhead vent stream,and forming a membrane feed vapor, and the membrane contacting themembrane feed vapor, thereby forming the permeate and the retentate. 18.A method of dehydrating a byproduct stream in ethanol production, themethod comprising: distilling a feed mixture including ethanol and waterwith at least two distillation units including a beer column in fluidcommunication with a first stripper-rectifier column to remove at leasta portion of the water from the feed mixture, the beer column forming abeer column stillage stream and a beer column vaporous overhead stream,and the first stripper-rectifier column forming a firststripper-rectifier bottom stream and a first stripper-rectifier vaporousoverhead stream; reboiling a portion of the beer column stillage streamto produce a first supplemental steam, wherein reboiling the portion ofthe beer column stillage stream is driven by heat supplied by aretentate, a bottom stream of a stripper/vaporizer of a separationsystem, a depressure stream formed by a molecular sieve unit, or asecond stripper-rectifier vaporous overhead stream formed by a secondstripper-rectifier column in fluid communication with the beer columnand the first stripper-rectifier column; forwarding the firstsupplemental steam to the beer column; and reboiling a portion of thestripper-rectifier bottom stream to produce a second supplemental steam;forwarding the second supplemental steam to the stripper-rectifiercolumn.
 19. The method of claim 18, further comprising: contacting themolecular sieve unit with a first byproduct stream comprising at leastone selected from the group consisting of a portion of the firststripper-rectifier vaporous overhead stream and a portion of the firstfusel oil stream, thereby forming a product stream; cyclicallycontacting the molecular sieve unit with at least a portion of theproduct stream to regenerate the molecular sieve unit, and form aregenerate stream; contacting a second byproduct stream comprising atleast one of (1) the regenerate stream and (2) at least a portion of thefirst fusel oil stream with the separation system, thereby forming apermeate and the retentate; and forwarding at least a portion of theretentate into the product stream.
 20. The method of claim 19, furthercomprising exchanging heat between at least a portion of the regeneratestream and the first stripper-rectifier bottom stream.
 21. The method ofclaim 18, wherein reboiling the portion of the beer column stillagestream is driven by heat supplied by the bottom stream of astripper/vaporizer of a separation system, the depressure stream formedby a molecular sieve unit, or the second stripper-rectifier vaporousoverhead stream formed by the second stripper-rectifier column in fluidcommunication with the beer column and the first stripper-rectifiercolumn.
 22. The method of claim 18, further comprising forwarding thefirst stripper-rectifier vaporous overhead stream to the secondstripper-rectifier column, and forwarding a second fusel oil streamformed by the second stripper-rectifier column to the separation system.23. The method of claim 18, wherein reboiling the portion of thestripper-rectifier bottom stream is driven by heat supplied by theretentate, the bottom stream of the stripper/vaporizer of the separationsystem, or the depressure stream formed by a molecular sieve unit.